The sudden birth and sudden death of thermal fidelity in a two-qubit XY model

TL;DR

This paper investigates how energy level crossings and thermal fidelity in a two-qubit XY model are affected by magnetic field anisotropy, revealing sudden changes in fidelity linked to the system's parameters.

Contribution

It introduces the analysis of thermal fidelity dynamics in a two-qubit XY model considering magnetic field anisotropy and explores the use of Yangian algebra as a control mechanism.

Findings

Energy level crossings depend on magnetic field anisotropy.

Thermal fidelity exhibits sudden birth and death phenomena.

Yangian generators can control fidelity transitions.

Abstract

We study the energy level crossings of the states and thermal fidelity for a two-qubit system in the presence of a transverse and inhomogeneous magnetic field. It is shown clearly the effects of the anisotropic factor of the magnetic field through the contour figures of energy level crossing in two subspaces, the isotropy subspace and anisotropy subspace. We calculate the quantum fidelity between the ground state and the state of the system at temperature $T$, and the results show the strong effect of the anisotropic factor again. In addition, by making use of the transition of Yangian generators in the tensor product space, we study the evolution of the thermal fidelity after the transition. The potential applications of Yangian algebra, as a switch to turn on or off the fidelity, are proposed.